1. Field of the Invention
The present invention relates generally to an operation device for a friction clutch. The friction clutch is arranged in the drive train of a motor vehicle, especially a utility motor vehicle, under a bell-shaped housing and between a combustion engine and a transmission, gear, shift gear or change gear. The operation device includes a clutch release sleeve arrangement, which clutch release sleeve arrangement can be moved essentially equiaxially or coaxially to the friction clutch to operate the friction clutch. The operation device also includes a positioning servo arrangement with a pneumatic power cylinder arrangement. The pneumatic power cylinder arrangement acts on the clutch release sleeve arrangement and can be operated by a control valve. The control valve is connected to a pneumatic source. The control valve operates the pneumatic power cylinder arrangement depending on a command variable, signal, reference variable input or control input, which command variable represents a desired position, and an actual value, which actual value represents the axial position of the clutch release sleeve arrangement with respect to the friction clutch.
2. Background Information
A known operation device is disclosed in German Patent No. 33 21 578 C2. The known operation device has a vacuum servo power assist as a positioning servo arrangement. The servo power assist, which is constructed similarly to a vacuum break power assist, is integrally formed with a pneumatic power cylinder and a control valve. The servo power assist is arranged outside of the bell-shaped housing. Two working chambers of the pneumatic power cylinder are separated by an axially movable piston and an elastic membrane. The working chamber which is designed as a vacuum chamber is connected to a suction pipe system of the combustion engine. The other working chamber, which serves as a control chamber, can either be connected to the vacuum chamber by means of the control valve, or to the atmosphere by means of a pressure compensation opening. The vacuum servo power assist is operated by a control rod, which control rod can be axially displaced by an electric motor driven cam, whereby said control rod strikes, hits or knocks against a valve gate of the control valve. The axial displacement of the control rod will effect a switching of the control valve in such a manner that the piston follows the movement of the control rod with power assist. Through an hydraulic master cylinder, the movement of the piston acts on a slave cylinder, which slave cylinder is arranged on the outside of the bell-shaped housing and is connected to the master cylinder. The slave cylinder then acts on a clutch release fork which is assigned to a clutch release sleeve arrangement. It is possible to perform an emergency operation of the clutch when the combustion engine is turned off, i.e., when there is no vacuum, because the control rod can act directly on the piston through the valve gate of the control valve.
Although the maintenance and, if required, the repair of the positioning servo arrangement of the known operation device is relatively simple because it is arranged outside of the bell-shaped housing, the entire operation device requires a relatively high mechanical effort because of the load transmission, power transmission or transmission of energy that is required in order to operate the clutch release sleeve arrangement towards the bell-shaped housing. The relatively high mechanical effort corresponds to equally high production costs and possibly also to an operational safety level that is insufficient for certain requirements. Furthermore, the positioning precision of the positioning Servo arrangement is limited by the components required for the transmission of the operating power into the bell-shaped housing, because of bearing play and similar situations.
A known device for the operation of the clutch release sleeve of a motor vehicle friction clutch through an hydraulic or pneumatic means of compression or compression medium is disclosed in German Patent No. 29 23 487 C2. German Patent No. 29 23 487 discloses a known device having a means of pressure-ring cylinder that is arranged concentrically to the cam shaft between a clutch release sleeve and a fixed or rigid support inside of the bell-shaped housing. The means of pressure-ring cylinder is delimited in the direction of the clutch release sleeve by a flexible annular membrane piston.
From German Patent No. 32 19 768 A1, a known pneumatic power-ring cylinder is disclosed. The pneumatic power-ring cylinder is also arranged inside the bell-shaped housing but acts directly on the pressure plate of the friction clutch. The pneumatic power-ring cylinder is compress ed for the coupling, i.e., as long as the clutch pedal is not compressed, and presses with its annular piston on the pressure plate, which pressure plate is biased toward the ring cylinder and against the clutch disk, and the clutch disk against the flywheel. To do so, compressed air supplied by a compressed air source is led into the pneumatic power-ring cylinder through a metering valve that can be operated by the clutch pedal as long as the clutch pedal is not pressed. When the clutch pedal is pressed, the excess pressure or overpressure in the pneumatic power-ring cylinder can escape to the outside through a pneumatic connection between the pneumatic power-ring cylinder and the metering valve from an exhaust opening of the metering valve that is arranged outside of the housing. A back-coupling of the position of the annular piston of the pneumatic power-ring cylinder or the pressure plate to the metering valve is not provided.
Furthermore, another known operation device of the type initially mentioned is attached to the out side of the bell-shaped housing as an integral unit. The known operation device comprises the pneumatic power cylinder, an hydraulic slave cylinder and the control valve. The piston of the pneumatic power cylinder is attached to a rod element which forms the piston of the hydraulic slave cylinder. The rod element is connected to a tappet, which tappet reaches into the inside of the bell-shaped housing and engages a clutch release fork. The clutch release fork is assigned to the clutch release sleeve arrangement. A master cylinder, which master cylinder can be operated by the clutch pedal, and a control opening or entry of the control valve are connected to the hydraulic slave cylinder. Depending on the hydraulic pressure at the control opening, the control valve controls the supply or feed or the discharge or deflation of compressed air into the pneumatic power cylinder from the pneumatic power cylinder in such a manner that a preset hydraulic pressure determined by a pressure spring arrangement occurs or ensues at the control opening. In this way, the hydraulic slave cylinder serves as a measuring cylinder which records or reads the position of the rod element and thus indirectly the position of the clutch release sleeve arrangement, with the exception of some inaccuracies attributable to the steering joint play. Although the maintenance and repair of this known operation device is relatively simple because said device is arranged on the outside of the bell-shaped housing, it also requires a high mechanical effort because of the load transmission into the bell, which results in the same disadvantages as in the case of German Patent No. 33 21 578 C2.